There exists a system for driving and/or supervising trains known under the (French) acronym SACEM for "System for Assisting in Driving, Operation, and Maintenance", which system comprises fixed installations along the track and control equipment in each train. The control equipment of any train on the railway network under SACEM control receives messages from the fixed installations describing portions of the network in "lengths" each comprising several "blocks" that the train will encounter on continuing its journey. The train driving system thus receives "invariants" relating to permanent information such as the locations of points, switches, signals, speed limits, gradients, etc., and "variants" relating to time-varying information, and in particular the current positions of points, switches, and signals. In addition, the train receives similar information from the track each time it goes past points, switches, signalling lights, and signs. By comparing the information received from these sources and integrating internal displacement data, the system is capable of locating the train relative to the network and consequently of adjusting the running of the train.
Such a system, and any similar system, naturally assumes that the control equipment of each train is initialized whenever it enters a network under SACEM control, thereby enabling the equipment, while the train is still outside the controlled network, to receive one or more messages adequately describing the length into which the train will go on entering the network so that said control equipment will be capable of running the train, and in particular of stopping it if the track is not free. Similarly, initialization is necessary if a train is reversed or uncoupled.
Such initialization must be performed under very strict safety conditions since an initialization error could cause a train to intrude dangerously onto the controlled network.
Numerous solutions have been proposed for solving the problem of transmitting messages from fixed installations to a train. For example, in the SACEM system, messages are transmitted by current induction using the rails. Security against possible falsification of a message is obtained by redundancy in the received messages. The information contained in each message is verified to determine whether the message corresponds to the environment as already established in the train control system on the basis of previously-received messages that have been accepted. A message that contradicts this environment is rejected.
On initialization, such precautions are not possible since the environment has not yet been established. In the SACEM system this has led to providing specific initialization means. These means are in the form of an initialization loop disposed between the rails at each inlet to the controlled network. This loop is fed with an alternating current and from place to place its wires cross over such that a coil mounted on a train and detecting the alternating current senses phase inversions which constitute coded information. Another loop is disposed between the rails parallel to the first and is read by a different coil and serves to provide reference information enabling the encoded information to be interpreted.
Such a system is satisfactory from the safety point of view. The signals from the two loops run no risk of being detected separately by the two initialization coils of a train running along a parallel track which could convey erroneous initialization information to that train. However, the system suffers from two constraints: specific initialization equipment needs to be mounted on each train, and a train must be moving in order to receive an initialization message.
Away from controlled networks, there also exists a system for transmitting messages from fixed installations to trains for the purpose of monitoring train speeds. At each transmission location, the system includes an elongate loop disposed on either side of a rail on the base of the rail and fed with a frequency modulated speed-monitoring carrier wave. This wave is detected by a speed-monitoring coil disposed on the train and facing the rail. In practice, two loops are disposed in parallel, one on each rail and the train carries two speed-monitoring coils, one per rail. Such a system is used merely for monitoring train speed and therefore has no direct influence on the running of the train, and as a result it does not need to offer a high degree of safety. In particular, it suffers from a danger of cross-talk, as explained below, and is therefore unsuitable for secure transmission of initialization messages.
The object of the present invention is therefore to provide an initialization system based on the second above-mentioned system but providing the required degree of security so that initialization can be performed without suffering from the constraints specified with respect to the first-mentioned system.
This provides considerable equipment saving in that the same transmission means are used for two purposes, and in operation it provides a considerable time saving since a train can be initialized while stationary, immediately prior to being authorized to move onto the controlled network.